What are the PC's specs: GPU/CPU/RAM?
What version of VP is being used? Try the latest. For licensed users upgrades are free for up to six months from purchase date. After that, VP will continue to fully function but a fee is required in order to register the newest. Retain your old install file and registration info. If there's an issue, you can always revert.
Never have run across your issue before. Does it occur if a single file is loaded, with no effects?
Go to OPTIONS | ADVANCED. In the GPU section at the bottom click the caret and choose NONE (CPU only).
Please answer the above queries and report results hre.